Fitze79, take your arguement on 12 month service based on normal usage, but the as per manuafacturers instructions is a 'minimum' of every 12 months.
Billo, stats provided by OFTEC (Oil Fired Technicians Ass.) supports the belief that you will pay MORE for your loss of efficiency than you will for your yearly service, and I would have thought with the cost of oil, the rise in awareness for our unique one of a kind blue planet and the need to protect it properly serviced oil burners are a small price to pay.
The hope is when regulated before end of 2009 your yearly service will be a requirement! or you may either incur a higher tax on your fuel or you supplier may not be able to supply you at all! (we live in hope)
Also remember, the service does more than just this, in a PROPER service
as well as having your boiler efficiency tested, you are also having your grennhouse gases tested (and set as low as they can go) and testing for carbonmonoxide is also performed, ensuring your well being.
Also, things like fire valves are checked, the condition of your oil tank, one local who didn't bother to have this checked ended up with a bill for €15000 last christmas when his 'improperly' installer oil tank leaked!